Commercial and industrial spray paint and powder coating booths in the United States and elsewhere are required by various regulations to prevent significant amounts of airborne liquid coating droplets (such as paint, varnish, and polymers) or dry powder from escaping into the atmosphere. In the United States, the Environmental Protection Agency issues National Emission Standards for Hazardous Air Pollutants (NESHAP), and 40 Code of Federal Regulations, Part 63 (40 C.F.R. 63) sets standards for air emissions.
Industrial filter manufacturers continuously seek to improve the particulate removal efficiency of filter media. One approach to improve the efficiency of a filter is by providing a denser medium with smaller pores. However, one problem with this approach is that it also increases the flow resistance, which increases the pressure drop across the filter medium.
Another method for enhancing the particulate removal efficiency of a fibrous filter is to spray a tackifier agent onto the filter medium after the non-woven fibrous web has been formed and the binder on the filter has been cured. For example, oil, chlorinated paraffin, or phosphate esters may be sprayed onto a filter medium web to promote the adhesion of particles and therefore improve filtration. However, the sprayed tackifier is concentrated near the surface of the filter medium and is nearly non-existent in the interior. It is impossible to penetrate such a spray into the interior of the filter medium using known methods except by the use of excessive quantities of tackifier and at very high pressures. Furthermore, attempting to utilize such large quantities and high pressure results in a product that is oily and difficult to handle.
To assist in the understanding of the principles disclosed herein, and without limiting the scope of the disclosure, the term “paint” will generally be used to represent liquid coatings and powder coatings generally applied to surfaces by a spray nozzle in a booth in commercial and industrial applications.
Air pollution standards require a minimum flow of air through the booth for the safety and comfort of operators inside the booth and for the proper application of the paint. To accomplish this, many types of paint arrestors have been variously made of paper, high-loft polyester, fiberglass, and other materials in multiple configurations and combinations.
As the paint arrestor media becomes saturated with paint, it ultimately impedes the flow of air through the air exit of the paint booth and must be replaced with fresh paint arrestor media. Maintenance schedules for commercial and industrial spray paint booths typically determine the economic benefit of various types of paint arrestors. Booth operators prefer to interrupt the painting operation as seldom as possible for paint arrestor changes. Booths in which relatively little paint is sprayed and which are not in continuous use can use paint arrestors with less paint holding capacity. Conversely, booths that spray high volumes of paint on a more continuous basis benefit economically from using paint arrestors that hold higher amounts of paint before clogging. Existing paint arrestor media suffer from face loading, in which an undesirably high percentage of the paint droplets, of all sizes, are captured and held at the surface of the media, resulting in air pathways that are prematurely clogged with paint.
Thus there remains a considerable need for paint arrestors with improved paint holding capabilities.